Implement Table Driven Test in Java

This entry is for GMO Ad Marketing Advent Calendar 2018 (Https://qiita.com/advent-calendar/2018/gmo-am) [12/09] article. This is the first GMO ad marketing entry in the Advent Calendar.

Introduction

In Go language, it is common to write test code in the form of Table Driven Test. The word "Go-ness" is often used among Go engineers. The source code is always required to be written like Go. I think there are some ambiguities in the word Go-ness, but Table Driven Test is one of Go's uniqueness. This time, I will introduce an example of bringing Go-ness to Java.

What is Table Driven Test?

The Table Driven Test is described on the following pages. https://github.com/golang/go/wiki/TableDrivenTests

In Table Driven Test, test cases are represented by a structure, which is looped to execute the test. This time, for the sake of explanation, I created a partial test of pow.go.

package main

import (
	"testing"
	"math"
)

func TestPow(t *testing.T) {
	for _, tt := range []struct {
		name     string
		x        float64
		y        float64
		expected float64
	}{
		{"Pow(2,1)", 2, 1, 2},
		{"Pow(2,2)", 2, 2, 4},
		{"Pow(2,3)", 2, 3, 8},
		{"Pow(2,0)", 2, 0, 1},
		{"Pow(2,-1)", 2, -1, 0.5},
		{"Pow(0,2)", 0, 2, 0},
		{"Pow(2,+Inf)", 2, math.Inf(0), math.Inf(0)},
		{"Pow(2,-Inf)", 2, math.Inf(-1), 0},
		{"Pow(+Inf,2)", math.Inf(0), 2, math.Inf(0)},
		{"Pow(-Inf,2)", math.Inf(-1), 2, math.Inf(0)},
	} {
		t.Run(tt.name, func(t *testing.T) {
			result := math.Pow(tt.x, tt.y)
			if result != tt.expected {
				t.Errorf("expected: %v, result: %v", tt.expected, result)
			}
		})
	}
}

In this example, the structure defines the test name, method arguments, and expected value. By writing like this, what each value represents It also makes it easier to see what you are testing.

Table Driven Test implemented in Java

Use the features added in JUnit 5 to implement Table Driven Test in Java.

This time I created a pow test for the Math class. The example uses lombok to keep the source code simple.

import lombok.AllArgsConstructor;
import lombok.Getter;
import lombok.experimental.Accessors;
import org.junit.jupiter.api.*;

import java.util.stream.Stream;

import static org.junit.jupiter.api.Assertions.assertEquals;

class MathTest {

    @Nested
    static class Pow {

        @AllArgsConstructor
        @Getter
        @Accessors(fluent = true)
        static class TestCase {
            private String name;
            private double x;
            private double y;
            private double expected;
        }

        @TestFactory
        Stream<DynamicNode> testPow() {
            return Stream.of(
                    new TestCase("pow(2,1)", 2, 1, 2),
                    new TestCase("pow(2,2)", 2, 2, 4),
                    new TestCase("pow(2,3)", 2, 3, 8),
                    new TestCase("pow(2,0)", 2, 0, 1),
                    new TestCase("pow(2,-1)", 2, -1, 0.5),
                    new TestCase("pow(2,+Inf)", 2, Double.POSITIVE_INFINITY, Double.POSITIVE_INFINITY),
                    new TestCase("pow(2,-Inf)", 2, Double.NEGATIVE_INFINITY, 0),
                    new TestCase("pow(+Inf,2)", Double.POSITIVE_INFINITY, 2, Double.POSITIVE_INFINITY),
                    new TestCase("pow(-Inf,2)", Double.NEGATIVE_INFINITY, 2, Double.POSITIVE_INFINITY)
            ).map(testCase -> DynamicTest.dynamicTest(
                    testCase.name(),
                    () -> {
                        double result = Math.pow(testCase.x(), testCase.y());
                        assertEquals(testCase.expected(), result);
                    })
            );
        }
    }

}

In JUnit 5, you can define an inner class with @ Nested to nest your tests. In this example, the test is defined by an inner class called Pow.

In Pow, we define an inner class called TestCase. The TestCase fields define the test name, the arguments to pass to the method, and the expected result. The value used in each test case is passed in the TestCase constructor.

If you use a class like Tuple here, It's hard to tell what each value you pass to Tuple represents, By having the test case in an inner class like the example You can associate a value with a named field.

We use JUnit 5's new Dynamic Tests (https://junit.org/junit5/docs/current/user-guide/#writing-tests-dynamic-tests) to run the tests. @testfactoryBy attaching to a method that returns a dynamic node stream, collection, etc. You can run the test dynamically.

Summary

By combining the features of JUnit 5 with the goodness of Go language, I was able to write a highly readable test in Java. It would be great if we could continue to incorporate the good points of other languages, such as Go-ness, into Java.

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